Device for phase modulation



July 24, 1951 ZSCHOKKE 2,561,455

DEVICE FOR PHASE MODULATION Filed March 5, 1948 Patented July 24, 1951 Dietlrelm'Zschokkep Solothurn; Switzerland; as-

signon to- Autophbn Aktiengesellschaft;RS011 thunn; Switzerland: .2

Application March. 1948,,fSerialfNo; 13,251

In Switzerland March '10," 1947 i i claimsit (o1. sass-2e) Circuits are lmown which enable to modulate the frequency of an alternating voltageby modulating its phase, the instantaneous phaseshift-being in advancewith a positive-modulat ingwoltage'and: in retardation with a negativemodulating voltage withs respect to the -carrienfrequency;-

For communication purposes, a it is desirableto apply phase departures of 800-. or-more angular degrees, i. e. the instantaneous advanceor retardation: of phase should total upi to several periods... The. technical modulation: methods will-show maximumeadvance: of 180; the ca'se of the susceptance being. equal to zero,. th'ere will be no. phaseshift and .if. the susceptanee is -made negative and infinite, the. phases shift' will show a maximum retardation; of 180 With -such circuit arrangements.- phase depar-- tures which exceed. for examplelBO and which. amount toa maximum. of 360 may be ob-i tainedi known up; BOr'IIOW- dO not enable touproduoes xiirectlynsuch considerable shifts. The phase departures obtainable. in known: circuitsw; and:

with a,.sufficient1y linear modulation .1 are iof; the

order; of. several degrees. phase: departures; of. several. hundred. degrees/s.v the carrier. frequencyis .kept small and .it; is sin-. creased after: modulation. the phase. shift' then;

In order tow obtain .1

being; increased r in. the. same. proportion. In

order not to be forcedto. apply too. largesanrinw crease-,., :the requirement is being. maintained thatphasedepartures as; high as1-p0ssible ShQilldiJi be; obtained. in the; modulation; A. furthersimultaneous, requirement. is. thatzthe'bphasew Shiftashquldi .be; i as; far as, possible directly or-in directly proportional to the instantaneous ivalue; a of; the modulating voltage, i. e.-,thatl the; moduw lation is linear as .far, as; possible;

A peculiaritypf, most of the knowmphase.

modulators isthat the modulation iS;-:I10tj an absolutely linear; function of the; modulating the arcus tangens law and-that it. issuificientliln EX'eeutional: forms. Ofuthe present invention are 'expla'inedi'by way of; example! and illustrated in theaccompanyingz drawing;

Figt 1 shows:thecircuitof a phase bridge with a variablev apparentm resistance,

Figsz xzi-and. 2a: show. variable loss-free react- 'ances-,=a U

Figsu: 3 1 and: 3m show: variable. loss-containing;v reactances,

Figs: 4 tshows a ,vector. diagram 1 of l the phase bridge withra i. variable lossefree reactance,

Fig. 5Tshows :a vector diagramwvith a variable lossscontaining reactance.

Thes'phase: bridge accordingtto Fig. 1 com,- prises-ivaivoltage divider'between the points a andsrb, consisting of the two fixed resistances. RKIgfiIldaRQie The arm;a-e contains a resistance R1-:,.-and:.the:-arme-7-b a variable reactance. It is-oflznc moment for. the invention whether the two ;resistances Ra. and R4 are real or. complex underathetconditionthat both are of equal mag-- nitude and-:in phasew The resistance R1 .isa pure;:resistance.- Forthe variable reactance the condition is hth at it. may assume positive and negative values. Such reactance is assumed to be loss-freer. Figs. 2 and 2a show two examples of such reactances; it being of no imof ,;th e 1' theoretically possible regions In .knownr,

phase :modulators, such theoretically phase .de-.----

partureamounts to 90.6or ;.in other circuits, a maximum of 180.

The. presentinvention-relates to a device for phase modulation, characterised in that the modulated voltagesis produced byx-means of a bridge circuit,,.arranged in; such a .manner that the maximum possible phase departuresofiflthes modulated voltage exceeds 180. This is old-'- tained in that-at-leastone -arm-of-the bridge comprises a variable reactance which isnara. ranged; f or; example. in such a manner thataits suscentance; may, be, made positive as wellzyas negative; thesothermpart operatingas fixed-voltagealdivi'der, whereby the input voltagajs; decomposediinto two equal in-phase: components; If;.the susceptance is made positivexandinfinite; them the phase shift of the modulatecttvoltage portance;=:whether inductancesflL and capacitancescearearrangedin parallelor in series; it is1how.everr,- practicallto have them inparallels ii l the; susceptancel-is considered and. to have M I them uin. series if reactance is. considered. 359' WfiYyOfiBi ZMZQBIB, the. capacitance C is assumed to zhe variable butlit is also .possibleto .choose.

a variable inductance, or to vary both. simul.-

varied, the magnitude and phase of voltage v2 varies with respect to the input voltage lie, the phase-shift through 90 with respect to voltage v1 remains and the magnitude and phase oft,

voltage 111 also varies with respect to theinput voltage ve. mains unvaried and shifts -in phase with respect to the input voltage ve. va (pointE) rotates along a circle with the voltage centre in D. In the position represented,

the point E corresponds to a positive reactance,

R2. If the reactance becomes infinite, the arrow tip 118. travels to A and the phase shift 6 be-.

comes +180; if the reactance becomes zero (=resonance)., the phase shift is also zero and the arrow tip coincides with B. If the reactance is negative, the arrow tip travels from Ila further to point E1 and the phase shift becomes negative, i. e. retarded. If the reactance is again infinite but negative, the arrow point. rotates to A and the phase shift becomes l80.

This explanation concerns a loss-free reactance.

If the reactance is loss-containing, it may be represented as a complex apparent resistance with a real and unreal part. Figs. 3 and 361. show,

by way of example, circuitsythe three quantities being again advantageously assumed in'parallel if the conductance is considered, or in series if the resistance is considered. Fig. shows the corresponding vector diagram in case of a series circuit. The voltage 112 across the loss-containing reactance consists of a component UR correboth voltages are generated across efiective re.-

sistances connected in series. The vectors v1 and 11B are on a straight line. The imaginary voltage point E is positioned on a circle with the distance AB as diameter, the distance AB again representing the sum ofthe two in-phase voltages v3" and vi. In the case of a loss-containing reactance R2 it is necessary to choose the resistance R4 in excess of R3 in such a manner that the following proportion is valid for the tensions:

U4-U3 P 211 v Such proportionality enables the arrow tip of the voltage vector v3 to be positionedin the centre of a circle passing through the points A and E. Now a voltage vs. phase-shifted through the angle a may again be tapped-between the points it and e of the bridge.

travels along a circle through the points A, E and with the centre in D. It will be noticed that the loss-containing part of reactance R2 does not disadvantageously influence the phase modulation, but only means a loss in the absolute value T of the tapped voltage.

If a parallel oscillatory circuit is used, the vector diagram of Figure 5 is reflected in point D.

I However, the voltage v corresponds to the volt--' age appearing over the resistance R1 and the voltage 111 corresponds to the voltage appearing" The magnitude of voltage Ua re The arrow tip of The compo- '60 By varying the reactance R2 from through zero to a phase-shift of volt-" age 119, from +l80 through axis AB to -'180 is again obtained and the arrow tip of vector Ua over the loss resistance of the parallel oscillating circuit. By analogy the value of the impedance R3 has to exceed that of R4 so that the following proportion is valid for the voltages:

Owing to the fact that the maximum phase departure, obtainable by means of the circuit arrangement according to the invention, in any case exceeds 180, it follows that the phase departure which may bepractically made use of with a greatest admissible distortion, is a multiple and at least the double of the phase departure of hitherto known circuits.

.What I claim is:

1. In an arrangement for phase modulation, in combination, a bridge circuit comprising four bridge branches, at least one of said brilge branches having an oscillating circuit the resonance frequency of which is variable, a pure efiective resistance in one of said branches and, awoimpedances of equal phase shift in adjacent bridge branches to form a voltage divider connected to the input voltage, the impedance adjacent the oscillating circuit being sufficiently larger than the other of said'impedances that the usuablevoltage for each phase angle has a constant amplitude.

bridge arms, one of said arms having 'a loss+ containing oscillatory circuit the resonant fre-' "l quencyof which is variable, an adjacent arm having a pure resistance and the remaining two.

arms having each an impedance of equal phase shift to form a voltage divider connected-to the input of the bridge, one of said impedances being i fsufficiently greater than the other of said im- 40 pedances that the usuable voltage for each phase angle has a constant amplitude.

3. In an arrangement according tothe claim 2,

e0 latory circuit to the said pure resistance.

4. In an arrangement according to claim 2, the 7 said oscillatory circuit being a parallel-oscillating i I circuit, the impedanceadjacent the said parallel-j 7 """oscillatory-circuit being smaller than the imped- -f ance adjacent the said pure resistance, and the ratio of the difference of said impedances to 3 double the said smaller impedance being equal to the ratio of the said-pure resistance to the loss .1

- resistance of said parallel oscillatory circuit.

REFERENCES CITED The following references are of me of this patent:

UNITED STATES PATENTS I Date Number Name 1,900,538 Bedford Mar. 7, 1933 I 1,901,694 I Bedf ord Mar. 14, 1933 1,950,406 I-Ioorn Mar. 13, 1934 2,042,234 Lyle May 26, 1936 2,045,107 Shore June 23, 1936' 2,125,127 I Roberts July 26, 1938 2,160,528 Uusselman .ll is May 30, 1939 2.: In an arrangement for phase modulation, in combination, a bridge circuit comprising four the said oscillatory circuit being a series oscillatory circuit, the impedance adjacent the said 5 45 series-oscillatory circuit being larger than the impedance'adjacent the said pure resistance, and the ratio of the difference of said impedances-te double the smaller impedance being equal to the 'ratio of the loss resistance of the said series oscil DIETI-IELM zscnoxxn.

record' in the 

